The prilling of molten materials hardenable upon cooling was well known. Typically, the molten material to be prilled was atomized with an inert gas in a nozzle to form droplets of liquid material which cooled and solidified as prilled particles. The size of the liquid droplets formed during the atomization generally determined the size of the prilled particles. For materials such as polyoxyethylene glycols, it was generally desired to form prilled particles with a fairly narrow size distribution, typically such that only relatively small proportions of the particles would be retained on a 10-12 mesh screen or passed through a 100 mesh screen, for example.
A major disadvantage of nozzles heretofore used for prilling was the failure to obtain an acceptably narrow size distribution of the prilled particles, typically necessitating classification of the particles subsequent to prilling and recycling a substantial portion of undersize and/or oversize particles to be reprilled.
Another disadvantage associated with such nozzles was excessive maintenance and lost production time caused by the fouling of the atomizing gas ports by liquid feed material entering into, hardening and plugging the gas ports, totally or partially, thereby adversely affecting the degree of atomization.
Yet another disadvantage was the lack of versatility of heretofore known prilling nozzles. Depending on the feed material, primarily its viscosity, the throughput, and the desired size distribution of the prilled particles, it was often necessary to make adjustments to the prilling nozzle, or to use a different nozzle, to prill different feed materials or to obtain a product of different particle size distribution.